1. FIELD OF THE INVENTION
This invention relates to a drive shaft of hollow form and made of fibre-reinforced plastics material. More particularly, the invention relates to the provision at an end of such a shaft of a connecting means by which a torque transmitting connection is established with the shaft. The invention also relates to a method of manufacturing such a shaft, and to a device for use in its manufacture.
A shaft according to the invention may be used as the propeller shaft of a motor vehicle.
2. DESCRIPTION OF PRIOR ART
In motor vehicle engineering, numerous attempts have been made to reduce vehicle weight and a particular reduction in weight can be achieved by use of a hollow shaft of fibre-reinforced plastics material. The problem with such shafts is the provision of a satisfactory torque transmitting connection at the end of the shaft, and there have been many proposals for such connections.
For example, DE-PS No. 3007896 proposes the use of a tubular metal sleeve having a flange formed at its end and with an internal profile such that, when it is axially slidden onto a pre-produced fibre-reinforced plastics shaft, the profile cuts into the shaft thereby establishing a driving connection.
In DE-OS No. 3421191, there is proposed the use of a tubular metal sleeve inserted into a hollow shaft and having a metal flange.
In DE-OS No. 2950581, there is proposed the use of a multi-component connecting element which is clamped to the end of a hollow fibre-reinforced plastics shaft.
In GB-OS No. 2146097, there is proposed the use of a metal connecting element with a flange portion and a tubular sleeve which is attached to the end of a shaft by incorporating it in the structure of the shaft while the shaft is being produced by helical winding of fibres impregnated with a hardenable resin.
All the above designs of connecting means for drive shafts made of fibre-reinforced plastics material have a disadvantage in that the use of a metal connecting element, usually with a flange portion, adds to the weight of the shaft and to some extent negates the potential weight saving. Further, the critical speed of the shaft with regard to bending thereof in use is reduced.
Furthermore, such prior art torque transmitting connections only introduce torque to the tubular shaft by way of the layer of fibres thereof which is nearest the tubular sleeve engaging the shaft. Torsional forces cause shear stresses between the layers of fibres forming the shaft, which stresses are at a maximum in the fibre layer immediately adjacent the tubular sleeve. The torque transmitting ability of the connection is determined by the inter-laminar shear strength of the layers of fibres constituting the shaft.